Transport system and transport method

ABSTRACT

In a transport system, a local track is disposed so as to be below an overhead travelling vehicle track in parallel or substantially in parallel therewith, and furthermore above a loading port of a processing device from upstream of the loading port to downstream of the loading port. A local vehicle including a hoist travels along the local track. Below the local track, a first buffer is disposed upstream of the loading port of the processing device, and a second buffer is disposed downstream of the loading port of the processing device, and the overhead travelling vehicle and the local vehicle can both perform delivery and receipt of the article with the first buffer and the second buffer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transport system, and in particularto a transport system that supplies and removes articles without causinga processing device to wait.

2. Description of the Related Art

There is a need for articles such as FOUPs (sealed cassettes fortransporting semiconductor wafers) to be supplied to and removed fromthe loading ports of devices such as a semiconductor machining deviceand a semiconductor inspection device without causing such devices towait. In view of this need, it has been proposed to provide a buffer inthe vicinity of a processing device, and provide an additional transportdevice for performing transport between the buffer and the processingdevice. For example, in JP 2006-224944A, multiple overhead travellingvehicle tracks are disposed in parallel in a ceiling space, one of whichis used for long-distance transport, and another of which is used forshort-distance transport. A buffer is disposed under the track forlong-distance transport, and the loading port of a processing device isdisposed under the track for short-distance transport. The overheadtravelling vehicle for long-distance transport performs the delivery andreceipt of articles with the buffer, and the overhead travelling vehiclefor short-distance transport performs the delivery and receipt ofarticles between the buffer and the loading port. Accordingly, ifarticles required by the processing device have been transported to thebuffer in advance, the articles can be quickly supplied to theprocessing device. Also, the overhead travelling vehicle forshort-distance transport quickly removes articles from the loading portof the processing device. However, this configuration requires providingtracks at the same height position in parallel, thus increasing thefloor space occupied by the transport system in a plan view.

In JP 2005-150129A, a buffer including a transport device is provided infront of a processing device, an overhead travelling vehicle performsthe delivery and receipt of articles with the buffer, and the transportdevice of the buffer performs the delivery and receipt of articles withthe loading port. However, a display for indicating the operation state,an operation panel for manual operation, and the like are provided onthe front surface of the processing device, and it is not preferable forthem to be blocked by the buffer. Also, the loading port is used notonly by an automatic transport device, but also for manual supply andremoval of articles, and manual access is difficult if the front surfaceof the processing device is covered by the buffer.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a transportsystem and method that swiftly supply articles to and remove articlesfrom a processing device without blocking the front surface of theprocessing device, while significantly reducing the amount of floorspace occupied by the transport system in a plan view.

In addition, preferred embodiments of the present invention minimize theamount of lifting/lowering when the delivery and receipt of articles isperformed with a buffer.

Furthermore, preferred embodiments of the present invention reduce andminimize the transport distance between a buffer and a loading port.

Additionally, preferred embodiments of the present invention provide aspecific configuration in which an overhead travelling vehicle performsthe delivery and receipt of articles with a buffer without interferencewith a local vehicle.

Various preferred embodiments of the present invention provide atransport system including, in order to transport an article between aplurality of processing devices, an overhead travelling vehicle trackthat passes above loading ports of the processing devices, and anoverhead travelling vehicle that travels in one direction along theoverhead travelling vehicle track and includes a hoist.

This system according to a preferred embodiment of the present inventionincludes a local track that is disposed so as to be below the overheadtravelling vehicle track and above a loading port of a processing devicefrom upstream of the loading port to downstream of the loading portalong the one direction, and is disposed in parallel or substantially inparallel with the overhead travelling vehicle track; a local vehiclethat travels along the local track and includes a hoist that lifts andlowers an article; a first buffer that is disposed so as to be below thelocal track and upstream of the loading port of the processing devicealong the one direction, the overhead travelling vehicle and the localvehicle both being able to perform delivery and receipt of an articlewith the first buffer; and a second buffer that is disposed so as to bebelow the local track and downstream of the loading port of theprocessing device along the one direction, the overhead travellingvehicle and the local vehicle both being able to perform delivery andreceipt of an article with the second buffer.

According to this configuration of a preferred embodiment of the presentinvention, the space where the overhead travelling vehicle travels andthe space where the local vehicle travels can be vertically overlappedwith each other, thus enabling a significant reduction in the amount offloor space occupied by the transport system in a plan view. Also, thefront surface of the processing device is not blocked by a buffer. Sincethe first buffer and the second buffer are provided upstream anddownstream of the loading port, the local vehicle can swiftly performthe supply and removal of articles between the loading port and thebuffers. The processing device may be provided with only one loadingport or multiple loading ports. In the case of providing multipleloading ports, the local track is provided from upstream of the loadingports to downstream of the loading ports, the first buffer is providedupstream of the loading ports, and the second buffer is provideddownstream of the loading ports.

Another preferred embodiment of the present invention relates to atransport system for addition on to an existing overhead travellingvehicle system. This system preferably includes a local track that isdisposed so as to be below an overhead travelling vehicle track andabove a loading port of a processing device from upstream of the loadingport to downstream of the loading port along one direction, and isdisposed in parallel or substantially in parallel with the overheadtravelling vehicle track; a local vehicle that travels along the localtrack and includes a hoist that lifts and lowers an article; a firstbuffer that is disposed so as to be below the local track and upstreamof the loading port of the processing device along the one direction, anoverhead travelling vehicle and the local vehicle both being able toperform delivery and receipt of an article with the first buffer; and asecond buffer that is disposed so as to be below the local track anddownstream of the loading port of the processing device along the onedirection, the overhead travelling vehicle and the local vehicle bothbeing able to perform delivery and receipt of an article with the secondbuffer.

This enables the transport system including the local track, the localvehicle, and the first and second buffers to be added on to an existingoverhead travelling vehicle system. Also, the add-on transport systemdoes not require processing device modification, and even when appliedto an existing overhead travelling vehicle system, the add-on transportsystem only requires modification for the shared use of struts. Also,the space where the overhead travelling vehicle travels and the spacewhere the local vehicle travels can be vertically overlapped with eachother, thus preventing the front surface of the processing device frombeing blocked by the buffers. Since the first buffer and the secondbuffer are provided upstream and downstream of the loading port, thelocal vehicle can swiftly perform the supply and removal of articlesbetween the loading port and the buffers.

Preferably, the first buffer and the second buffer are each configuredsuch that one article can be placed thereon. This enables disposing of atotal of two buffers respectively upstream and downstream of the loadingport, while being adjacent to the loading port.

Preferably, the first buffer and the second buffer are each disposed ata height according to which the local vehicle supporting an article maytravel only above the first buffer without an article and the secondbuffer without an article, and the local vehicle not supporting anarticle may travel the first buffer both with an article and without anarticle and the second buffer both with an article and without anarticle. This enables the local vehicle to swiftly transport articles toand from the buffers.

Also, preferably, the first buffer and the second buffer each have atwo-level stepped structure including an upper level and a lower level,and one article can be placed on each of the upper level and the lowerlevel of the first buffer and the second buffer, the lower level isdisposed on a side close to the loading port, the upper level isdisposed on a side distant from the loading port, and regardless ofwhether an article has been placed on the lower level, the local vehiclecan pass above the lower level when the local vehicle is supporting anarticle and when the local vehicle is not supporting an article, and theupper level is disposed at a height according to which the local vehiclesupporting an article may travel only above the upper level without anarticle, and the local vehicle not supporting an article may travelabove the upper level both with an article and without an article. Thisenables disposing of buffers with a total capacity of four articlesupstream and downstream of the loading port, and furthermore enables thelocal vehicle to swiftly transport articles to and from the upper levelbuffer.

Also, preferably, the local track includes two parallel or substantiallyparallel rails with a gap in-between through which an article can passin a vertical direction provided between the two rails. According tothis configuration, even if the local track is disposed under the firsttrack, the overhead travelling vehicle can perform the delivery andreceipt of articles between the loading port and the buffers.

Preferably, the overhead travelling vehicle delivers an article to thefirst buffer and the second buffer and removes an article from theloading port, and the local vehicle delivers an article from the firstbuffer and the second buffer to the loading port. This control isexecuted by, for example, a controller of the overhead travellingvehicle and a controller of the local vehicle. According to thisconfiguration, articles are swiftly transported from the loading port,and the overhead travelling vehicle can drop off articles at the buffersregardless of whether an article is placed on the loading port. Then, ifthe loading port is empty, an article can be swiftly delivered from abuffer to the loading port.

Preferably, the first buffer and the second buffer are supported by ahorizontal frame disposed above the loading port, and the frame isprovided with a look-down sensor to detect an interfering object on theloading port side. Due to the look-down sensor, the overhead travellingvehicle and the local vehicle do not interfere with, for example, aperson on the loading port side. Here, the “loading port side” refers tothe vicinity or the neighborhood of the loading port.

Also, a transport system according to a further preferred embodiment ofthe present invention is a transport system including a local track thatis disposed so as to be below the overhead travelling vehicle track andabove a loading port, and is disposed in parallel or substantially inparallel with the overhead travelling vehicle track; a local vehiclethat travels along the local track and includes a hoist that lifts andlowers an article; and a two-level stepped buffer including an upperlevel and a lower level, one article being able to be placed on each ofthe upper level and the lower level, the lower level being disposed on aside close to the loading port, the upper level being disposed on a sidedistant from the loading port, and regardless of whether an article hasbeen placed on the lower level, the local vehicle being able to passabove the lower level when the local vehicle is supporting an articleand when the local vehicle is not supporting an article, and the upperlevel being disposed at a height according to which the local vehiclesupporting an article may travel only above the upper level without anarticle, and the local vehicle not supporting an article may travelabove the upper level both with an article and without an article.

As an example of a stepped buffer, at least either the combination ofbuffers 25 a and 26 a or the combination of buffers 25 b and 26 b shownin FIG. 1 is provided.

According to this configuration, the space where the overhead travellingvehicle travels and the space where the local vehicle travels can bevertically overlapped with each other, thus enabling a significantreduction in the amount of floor space occupied by the transport systemin a plan view. Also, the front surface of the processing device is notblocked by a buffer. Also, since the buffers are arranged in a steppedfashion, namely in an upper level and a lower level, the overheadtravelling vehicle and the local vehicle can span access both the upperand lower levels, and since the height level difference between thelocal track and the upper level buffer is small, articles can besupplied to and removed from the upper level buffer with a small amountof lifting/lowering.

Also, a transport method according to yet another preferred embodimentof the present invention is a transport method for transporting anarticle to a loading port of a processing device using an overheadtravelling vehicle track that passes above the loading port and anoverhead travelling vehicle that travels in one direction along theoverhead travelling vehicle track and includes a hoist, a local track isdisposed so as to be below the overhead travelling vehicle track andabove the loading port of the processing device from upstream of theloading port to downstream of the loading port along the one direction,and is disposed in parallel or substantially in parallel with theoverhead travelling vehicle track, a local vehicle travels along thelocal track and includes a hoist that lifts and lowers an article, afirst buffer is disposed so as to be below the local track and upstreamof the loading port of the processing device along the one direction,the overhead travelling vehicle and the local vehicle both being able toperform delivery and receipt of an article with the first buffer, and asecond buffer is disposed so as to be below the local track anddownstream of the loading port of the processing device along the onedirection, the overhead travelling vehicle and the local vehicle bothbeing able to perform delivery and receipt of an article with the secondbuffer.

The transport method includes a step performed by the overheadtravelling vehicle for dropping off an article at the first buffer orthe second buffer; a step performed by the local vehicle for droppingoff an article from the first buffer or the second buffer at the loadingport; and a step performed by the overhead travelling vehicle forremoving an article from the loading port.

According to this configuration, articles are swiftly transported fromthe loading port, and the overhead travelling vehicle can drop offarticles at the buffers regardless of whether an article is placed onthe loading port. Then, if the loading port is empty, an article can beswiftly delivered from a buffer to the loading port.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of relevant portions of a transport systemaccording to a preferred embodiment of the present invention.

FIG. 2 is a plan view of relevant portions showing a state in whichtravelling rails of an overhead travelling vehicle have been removedfrom the transport system according to a preferred embodiment of thepresent invention.

FIG. 3 is a front view of a structure of a local vehicle.

FIG. 4 is a diagram illustrating communication within the transportsystem.

FIG. 5 is a front view of relevant portions of a transport systemaccording to a variation of a preferred embodiment of the presentinvention.

FIG. 6 is a side view of relevant portions of a transport systemaccording to another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes various preferred embodiments of the presentinvention. The scope of the present invention is based on the claims,and is intended to be determined in accordance with the understanding ofa person skilled in the art with reference to the description of variouspreferred embodiments of the present invention and related art in thefield of the present invention.

FIGS. 1 to 5 show a transport system according to preferred embodimentsand variations thereof. In these figures, reference numeral 2 denotes atransport system, and reference numeral 4 denotes a processing device,examples of which include a semiconductor processing device and asemiconductor inspection device. The transport system 2 is preferablyprovided in a clean room, for example. The processing device 4 includesone or more loading ports 6, and a track 10 for an overhead travellingvehicle 12 is provided over the loading ports 6 by being supported fromthe ceiling by struts 11. The overhead travelling vehicle 12 includes ahoist 14, which lifts and lowers an elevation platform 16 together witharticles 18. Here, the articles 18 preferably are FOUPs accommodating asemiconductor wafer, for example, but the articles 18 may be of anytype. In addition to the hoist 14, the overhead travelling vehicle 12may also include, for example, a device that transversely feeds of thehoist 14 and a device that pivots the hoist 14 about a vertical axis.The track 10 and the overhead travelling vehicle 12 configure anoverhead travelling vehicle system, and this system itself iswell-known.

Local tracks 20 are provided under the track 10, for example, and onelocal track 20 is preferably provided for each processing device, forexample. Although a local track 20 is provided in a range including theregion over the loading ports 6 and regions on both the left and rightthereof, for example, a local track 20 may be provided in a rangeincluding the region over the loading ports 6 and a region on either theleft or right thereof. Reference numeral 22 denotes a local vehicle thatmoves back and forth along the local track 20 and lifts and lowers anelevation platform 23 via suspending members 24 such as belts, wires, orropes, for example. Two types of buffers 25 a and 25 b, and 26 a and 26b are provided, for example, in front of and behind the loading ports 6in terms of the travelling direction of the local vehicle 22. Theoverhead travelling vehicle 12 travels in the direction indicated by thearrow in FIG. 1, and for example, the buffers 25 a and 26 a upstream ofthe pair of loading ports 6 configure a first buffer, and the buffers 25b and 26 b downstream of the pair of loading ports 6 configure a secondbuffer.

The buffers 25 a and 25 b are provided at a height position according towhich the local vehicle 22 can pass over the buffers 25 a and 25 bwithout interference when the local vehicle 22 is supporting an article18, and are provided at positions adjacent to the loading ports 6 in aplan view. In other words, a height difference greater than the heightof one article 18 is provided between the bottom surface of the article18 supported by the local vehicle 22 and the article placement surfaceof the buffers 25 a and 25 b. The buffers 26 a and 26 b configure thesecond buffer, and are provided on sides of the buffers 25 a and 25 bopposite to the loading ports 6. The buffers 26 a and 26 b are providedat a height according to which the local vehicle 22 can travel over thebuffers 26 a and 26 b when the local vehicle 22 is not supporting anarticle 18, and the local vehicle 22 cannot travel over the buffers 26 aand 26 b when the local vehicle 22 is supporting an article 18. In otherwords, the height difference between the bottom surface of the article18 supported by the local vehicle 22 and the article placement surfaceof the buffers 26 a and 26 b is less than or equal to the height of onearticle 18. For example, the buffers 26 a and 26 b are provided at aheight position that is higher than that of the buffers 25 a and 25 b bythe height of one article 18, thus configuring a one-level leveldifference between the buffers 25 a and 25 b and the buffers 26 a and 26b. Also, the buffers 25 a and 25 b and the buffers 26 a and 26 b aresupported by struts 27 and 28, and although the struts 27 are also usedas struts for the local track 20, for example, the struts 27 may beseparate from the struts for the local track 20.

Although the buffers 25 a and 25 b and the buffers 26 a and 26 b areprovided on both the left and right of the loading ports 6 (both infront of and behind the loading ports 6 in terms of the travellingdirection of the overhead travelling vehicle 12) in the presentpreferred embodiment, such buffers may be provided on only either theleft or the right. If the buffer capacity is insufficient, aconfiguration is possible in which, as shown by the chain lines in FIG.1, the buffers 26 a and 26 b are moved to the positions of buffers 31,and buffers 30 are provided below the original positions of the buffers26 a and 26 b. In this case, the local track 20 is also extended to theregions over the buffers 31.

If the buffers 25 a, 25 b, 26 a, 26 b, and the like are disposed asdescribed above, the overhead travelling vehicle 12 and the localvehicle 22 can deliver articles 18 to and receive articles 18 from anyof the buffers 25 a, 25 b, 26 a, and 26 b. Since the buffers 25 a and 25b are at a low position, they can be freely accessed by the overheadtravelling vehicle 12 and the local vehicle 22, but the amount oflifting/lowering during the delivery and receipt of the articles 18 ishigh. If the buffers 26 a and 26 b are empty, they can be accessed bythe load-bearing local vehicle 22 and the load-bearing overheadtravelling vehicle 12. If articles 18 have been placed on the buffers 26a and 26 b, they can be accessed by the non-load-bearing local vehicle22 and the non-load-bearing overhead travelling vehicle 12. Note thatthe overhead travelling vehicle 12 lifts and lowers the articles 18 viaa gap in the local track 20, which includes a pair of travelling rails,and the mechanism for achieving this will be described later.

As a result, the buffers 25 a, 25 b, 26 a, and 26 b can be accessed bythe local vehicle 22 and the overhead travelling vehicle 12. Since thebuffers 26 a and 26 b are at a higher position than the buffers 25 a and25 b, the movement time of the overhead travelling vehicle 12 and thelocal vehicle 22 can be shortened. Particularly with the local vehicle22, the amount of lifting/lowering during the movement of articles 18 islow, and the movement time can be shortened. Also, since the buffers 25a, 25 b, 26 a, and 26 b are placed in the vicinity of the loading ports6, the local vehicle 22 can transport articles 18 between the loadingports 6 and the buffers 25 a, 25 b, 26 a, and 26 b in a short time.

FIG. 2 is a view looking downward along the line II-II in FIG. 1, andthe transport system 2 is shown without the overhead travelling vehicle12 and the track 10. As shown in FIG. 2, the local track 20 preferablyincludes a pair of rails, and a gap 34 is provided between the rails.The width of the gap 34 is greater than the depth of the articles 18,and the articles 18 can pass through the gap 34 in the verticaldirection. Also, a charging device 36 that charges the local vehicle 22is provided above a loading port 6. Although the charging device 36 ispreferably disposed over one of the loading ports 6 in FIGS. 1 and 2,the charging device 36 may be disposed above the other loading port,between the pair of loading ports 6, or the like.

Except for the case of an article needed immediately by a processingdevice 4, the overhead travelling vehicle 12 drops off articles 18 onthe buffers 25 a, 25 b, 26 a, and 26 b. Also, except for the case of anarticle needed immediately by the next processing device, the overheadtravelling vehicle 12 removes articles from the buffers 25 a, 25 b, 26a, and 26 b instead of removing articles from the loading ports 6. Also,the transport of articles between the loading ports 6 and the buffers 25a, 25 b, 26 a, and 26 b is basically performed by the local vehicle 22.As a result, even if the local vehicle 22 stops above a loading port 6for charging, there is no interference with the transport of articles bythe overhead travelling vehicle 12. Note that the charging device 36 maybe provided at, for example, a position facing the buffer 25 a, 25 b, 26a, or 26 b. In this case, if the local vehicle 22 stops at that positionfor an extended time for charging, access to the buffer by the overheadtravelling vehicle 12 is hindered.

FIG. 3 shows the structure of the local vehicle 22, and in this figure,reference numerals 38 denote running wheels that are driven by a runningmotor 40, and reference numeral 42 denotes a battery that is charged bythe charging device 36 via a power receiving device 43. In place of thebattery, another power storage member such as a capacitor may be used,for example. Electricity may be supplied to the power receiving device43 via, for example, non-contact electricity feeding or contactelectricity feeding via a connector, a charging coupler, or the like.Reference numeral 44 denotes a hoist that lifts and lowers the elevationplatform 23, and reference numerals 45 denote chucks that grab andrelease flanges at the top of the articles 18.

FIG. 4 illustrates communication in the transport system, and anoverhead travelling vehicle controller 50 communicates with the overheadtravelling vehicle 12 and issues transport commands. For example, thecharging device 36 also functions as a controller for the local vehicle22, and by communicating with the overhead travelling vehicle controller50 via a communication unit 51, the charging device 36 reports thepresence or absence of articles 18 on the buffers 25 a, 25 b, 26 a, and26 b, the IDs thereof, and the like to the overhead travelling vehiclecontroller 50. The charging device 36 also receives, from the overheadtravelling vehicle controller 50, instructions regarding the transportof the articles 18 via the buffers 25 a, 25 b, 26 a, and 26 b. Acommunication unit 52 communicates with the overhead travelling vehicle12, and performs interlocking when the overhead travelling vehicle 12delivers articles 18 to and receives articles 18 from the buffers 25 a,25 b, 26 a, and 26 b. A communication unit 53 communicates with acommunication unit 54 of the local vehicle 22, and instructs the localvehicle 22 to move articles 18 between the buffers 25 a, 25 b, 26 a, and26 b and the loading ports 6.

The following describes operations performed in the transport system 2.An operation performed by the transport system is to supply an article18 to a loading port 6 exactly when the article 18 is required by theprocessing device 4, and to take an article 18 outside of the processingdevice 4 immediately when the article 18 is removed from the interior tothe loading port 6. In order to achieve this, it is sufficient toprovide a local vehicle 22 and buffers 25 a, 25 b, 26 a, and 26 bexclusively for the processing device 4. It is sufficient for articles18 required by the processing device 4 to be held on the buffers 25 a,25 b, 26 a, and 26 b in advance, and to transport the articles 18 to theloading ports 6 when they are required by the processing device 4. Also,it is sufficient for articles 18 that have been removed from theinterior to the loading ports 6 to be immediately moved to the buffers25 a, 25 b, 26 a, and 26 b by the local vehicle 22. Also, the transportof articles 18 to a position farther than the buffers 25 a, 25 b, 26 a,and 26 b is performed by the overhead travelling vehicle 12, which canalso access any of the buffers 25 a, 25 b, 26 a, and 26 b, and candirectly access the loading ports 6 as well in an urgent situation orthe like.

There are cases where an article 18 required by the processing device 4has not been placed on the buffer 25 a, 25 b, 26 a, or 26 b when it isrequired. In such a case, the waiting time of the processing device 4can be shortened if the overhead travelling vehicle 12 can directly dropoff articles 18 at the loading ports 6. Also, if the removal of anarticle required by the next processing device is delayed, the waitingtime of the next processing device can be shortened if the overheadtravelling vehicle 12 directly removes articles 18 from the loadingports 6.

The local vehicle 22 travels a short distance along the local track 20,and therefore needs only be a simple vehicle. Communication with thecharging device 36 serving as a controller is performed by, for example,use of the local track 20 as a signal line, providing a feeder linealong the local track 20, or performing radio communication between thevehicle 22 and the charging device 36. Also, the struts 27 and the likecan be used to supply power to the charging device 36, and can be usedas lines for communication with the overhead travelling vehiclecontroller 50.

Although the example of disposing the local track 20 preferably underthe track 10 is described in the present preferred embodiment, there isno limitation to this. FIG. 5 shows an example in which the local track20 is not disposed under the track 10, and in this figure, the samereference numerals as those in the above preferred embodiment denote thesame constituent elements. Reference numeral 60 denotes a new localtrack that is disposed below the track 10 while not being directly underthe track 10, and reference numeral 62 denotes a new local vehicle. Thelocal vehicle 62 is supported by the local track 60 via guide rollers 63to 65 and travels along the local track 60, reference numerals 67 and 68denote new struts, and the other aspects of this variation are similarto the preferred embodiment shown in FIGS. 1 to 4.

FIG. 6 shows another preferred embodiment of the present invention. InFIG. 6, reference numerals that are the same as those in FIGS. 1 to 4denote the same constituent elements, and aspects other than thoseparticularly pointed out below are similar to the preferred embodimentshown in FIGS. 1 to 4. The overhead travelling vehicle 12 travels in onedirection along the arrow shown in FIG. 6. The processing device 4includes a pair of loading ports 6, for example, a first buffer 70 isprovided upstream of the loading ports 6 in terms of the travellingdirection of the overhead travelling vehicle 12, and a second buffer 71is provided downstream of the loading ports 6 in terms of the travellingdirection of the overhead travelling vehicle 12. Note that the number ofloading ports 6 provided for each processing device 4 is arbitrary. Thelocal track 20 extends from a region above the first buffer 70 upstreamof the loading ports 6 to a region above the second buffer 71 downstreamof the loading ports 6. Reference numeral 72 denotes a horizontal framethat is supported by the struts 27, and the frame 72 extends from theregion above the loading ports 6 to regions on the left and right(upstream and downstream) thereof and supports the buffers 70 and 71.The buffers 70 and 71 are disposed at a height according to which thelocal vehicle 22 can travel over the buffers 70 and 71 when localvehicle 22 is not supporting an article 18, and the local vehicle 22cannot travel over the buffers 70 and 71 when the local vehicle 22 issupporting an article 18.

In a plan view, the track 10, the track 20, and the buffers 70 and 71overlap each other, and the loading ports 6 are under the tracks 10 and20. The track 20 preferably includes two rails, and a gap is providedbetween the rails such that articles 18 can pass between the rails inthe vertical direction. The local vehicle 22 stops at, for example, fourstop positions along the track 20, a charging device 74 such as acharging coupler is provided at each of the stop positions, and thecharging devices 74 charge a battery such as a lithium ion battery or acapacitor such as an electric double layer capacitor of the localvehicle. The local vehicle 22 can be charged each time it stops, andtherefore can be driven with a low-capacity battery or a low-capacitycapacitor. Note that a configuration is possible in which the chargingdevices 74 are provided at only positions over the buffers 70 and 71since it is not suitable for the standby positions of the local vehicle22 to be positions over the loading ports 6.

Reference numeral 73 denotes a controller that controls the localvehicle 22 and performs communication with the overhead travellingvehicle 12 or the overhead travelling vehicle controller 50 shown inFIG. 4. The frame 72 includes, for example, a pair of look-down sensors76 above the loading ports 6, and the look-down sensors 76 monitorinterfering objects such as workers in the vicinity of the loading ports6. The look-down sensors 76 each include, for example, a laser beamsource, a mechanism that scans the range indicated by chain lines inFIG. 6 by changing the orientation of a laser beam, and a photoreceptionelement arranged to receive reflected light. The look-down sensors 76monitor objects in the chain line ranges shown in FIG. 6, for example,and if an object is detected in a chain line range, the controller 73prohibits transport between the corresponding loading port 6 and thelocal vehicle 22 and overhead travelling vehicle 12. Note that onelook-down sensor 76 may monitor multiple loading ports 6. Also, thecontroller 73 may communicate with the overhead travelling vehicle 12via the overhead travelling vehicle controller 50 shown in FIG. 4instead of by direct communication.

The following describes operations performed in the present preferredembodiment. The overhead travelling vehicle 12 drops off (delivers)articles 18 on the buffers 70 and 71, and removes (picks up) articles 18from the loading ports 6. If a free space is available on the buffer 70,and an article 18 is to be removed from the loading port 6, the overheadtravelling vehicle 12 drops off a transported article 18 at the buffer70, and removes the article 18 from the loading port 6. Accordingly,delivery and removal can be performed by a single overhead travellingvehicle 12. The local vehicle 22 delivers articles on the buffers 70 and71 to the loading ports 6. The local vehicle 22 alternately changes itsstandby position above the buffers 70 and 71. For example, the localvehicle 22 waits above the buffer 70 after delivering an article on thebuffer 71 to a loading port 6, and thus the local vehicle 22 cansubsequently swiftly deliver an article on the buffer 70 to a loadingport 6. Note that if no articles 18 are present on the buffers 70 and71, the overhead travelling vehicle 12 may wait above the buffer 71 soas to be able to drop off an article 18 on the buffer 70. If there isthe risk of an overflow of articles 18 at a loading port 6, the localvehicle 22 may remove an article from the loading port 6 and deliver itto the buffer 70 or 71. Also, in the case of an urgent article, theoverhead travelling vehicle 12 may deliver an article directly to aloading port 6.

In the present preferred embodiment, the buffers 70 and 71 arepreferably adjacent to the loading ports 6, and the height differencebetween the track 20 and the buffers 70 and 71 is small. Accordingly,the local vehicle 22 can deliver articles 18 from the buffers 70 and 71to the loading ports 6 in a short time. From the viewpoint of theoverhead travelling vehicle 12, it is as if the processing device 4 hastwo loading ports exclusively for removal, and two loading portsexclusively for delivery. This enables a significant reduction andminimization of the occurrence of the problem that an article 18 cannotbe dropped off at a loading port 6. Also, from the viewpoint of theprocessing device 4, up to two articles to be processed can be stored onthe buffers 70 and 71.

The above-described preferred embodiment achieves at least the followingadvantages.

The buffers 25 a, 25 b, 26 a, and 26 b can be provided without blockingthe front surface of the processing devices 4.

The space where the overhead travelling vehicle 12 travels and the spacewhere the local vehicle 22 travels can be vertically overlapped witheach other, thus enabling significant reduction in the amount of floorspace occupied by the transport system in a plan view.

The buffers 25 a, 25 b, 26 a, and 26 b are arranged in a two-levelstepped fashion, namely in an upper level and a lower level, thusenabling the overhead travelling vehicle 12 and the local vehicle 22 toaccess any of the buffers 25 a, 25 b, 26 a, and 26 b. In particular, theheight level difference between the local track 20 and the buffers 26 aand 26 b is small, thus enabling articles 18 to be supplied to andremoved from the buffers 26 a and 26 b with a small amount oflifting/lowering.

Articles 18 can pass through the gap 34 provided in the local track 20,thus enabling the local track 20 and the buffers 25 a, 25 b, 26 a, and26 b to be disposed under the track 10 for the overhead travellingvehicle 12.

It is possible to add on the transport system made up of the local track20, the local vehicle 22, and the buffers 25 a, 25 b, 26 a, and 26 bwith almost no modifications to the processing devices 4 and theexisting overhead travelling vehicle system.

The local vehicle 22 moves back and forth along the short local track20, thus enabling swiftly performing the supply and removal of articlesbetween the loading ports 6 and the buffers 25 a, 25 b, 26 a, and 26 b.In particular, if the buffers 25 a and 25 b and the buffers 26 a and 26b are provided in front of and behind the loading ports 6, a largenumber of the buffers 25 a, 25 b, 26 a, and 26 b can be provided in thevicinity of the loading ports 6.

If the charging device 36 is provided above a loading port 6, thebattery 42 of the local vehicle 22 can be charged without hinderingaccess to the buffers 25 a, 25 b, 26 a, and 26 b by the overheadtravelling vehicle 12. Also, since the local vehicle 22 is driven usinga battery, there is no need to provide the local track 20 with anelectricity feeding rail.

Note that it is not necessary to provide all of the processing devices 4with the system that includes the buffers 70 and 71, the local track 20,and the local vehicle 22. For example, it is possible to provide such asystem for only processing devices 4 that process a large number ofarticles 18. The type of article 18 that is transported is arbitrary,and non-limiting examples thereof preferably include a cassetteaccommodating a semiconductor exposure reticle, and a flat panel displaysubstrate.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A transport system to transport articles among aplurality of processing devices, the transport system comprising: anoverhead travelling vehicle track passing above loading ports of theplurality of processing devices; an overhead travelling vehicletravelling in one direction along the overhead travelling vehicle trackand including a hoist; a local track disposed so as to be below and inparallel or substantially in parallel with the overhead travellingvehicle track and above a loading port of one of the processing devicesfrom upstream of the loading port to downstream of the loading portalong the one direction; a local vehicle travelling along the localtrack and including a hoist that lifts and lowers one of the articles; afirst buffer disposed so as to be below the local track and upstream ofthe loading port of the one of the processing devices along the onedirection, the overhead travelling vehicle and the local vehicle bothconfigured to deliver and receive one of the articles with the firstbuffer; and a second buffer disposed so as to be below the local trackand downstream of the loading port of the one of the processing devicesalong the one direction, the overhead travelling vehicle and the localvehicle both configured to deliver and receive one of the articles withthe second buffer; wherein in a plan view of the transport system, thefirst and second buffers are arranged to not overlap the loading port ofthe one of the processing devices in a vertical direction; in a sideview of the transport system, the first and second buffers are onlyprovided either in front of or behind the loading port in the onedirection; the first buffer includes a first sub-buffer and a secondsub-buffer disposed in a first two-level stepped arrangement; the secondbuffer includes a third sub-buffer and a fourth sub-buffer disposed in asecond two-level stepped arrangement; and the first and second two-levelstepped arrangements each include an upper level and lower level.
 2. Thetransport system according to claim 1, wherein the first buffer and thesecond buffer are each configured such that only one of the articles maybe placed thereon.
 3. The transport system according to claim 2, whereinthe first buffer and the second buffer are each disposed at a heightaccording to which the local vehicle supporting one of the articles maytravel only above the first buffer without any of the articles and thesecond buffer without any of the articles, and the local vehicle notsupporting any of the articles may travel the first buffer both with oneof the articles and without any of the articles and the second bufferboth with the one of the articles and without any of the articles. 4.The transport system according to claim 1, wherein the upper level andthe lower level of the first buffer and the second buffer are arrangedsuch that one of the articles can be placed on each of the upper leveland the lower level of each of the first buffer and the second buffer,the lower level is disposed on a side adjacent to the loading port ofthe one of the processing devices, the upper level is disposed on a sidespaced from the loading port, and regardless of whether one of thearticles has been placed on the lower level, the local vehicle may passabove the lower level when the local vehicle is supporting one of thearticles and when the local vehicle is not supporting any of thearticles, and the upper level is disposed at a height according to whichthe local vehicle supporting the article may travel only above the upperlevel without any of the articles, and the local vehicle not supportingany of the articles may travel above the upper level both with one ofthe articles and without any of the articles.
 5. The transport systemaccording to claim 1, wherein the local track includes two parallel orsubstantially parallel rails with a gap in-between through which thearticles can pass in the vertical direction.
 6. The transport systemaccording to claim 1, further comprising: a controller arranged andprogrammed to control the overhead travelling vehicle and the localvehicle such that the overhead travelling vehicle delivers one of thearticles to the first buffer and the second buffer and removes the oneof the articles from the loading port of the one of the processingdevices, and the local vehicle delivers the one of the articles from thefirst buffer and the second buffer to the loading port.
 7. The transportsystem according to claim 1, wherein the first buffer and the secondbuffer are supported by a horizontal frame disposed above the loadingport of the one of the processing devices, and the frame is providedwith a look-down sensor to detect an interfering object on the loadingport side.
 8. The transport system according to claim 1, furthercomprising: a controller configured or programmed to control theoverhead travelling vehicle and the local vehicle such that the overheadtravelling vehicle drops off one of the articles at the first buffer orthe second buffer, the local vehicle drops off the one of the articlesfrom the first buffer or the second buffer at the loading port of theone of the processing devices, and the overhead traveling vehicleremoves the one of the articles from the loading port.
 9. The transportsystem according to claim 1, wherein: the lower level of each the firstand second two-level stepped arrangements is arranged to be closer tothe loading port of the one of the processing devices than the upperlevel of each the first and second two-level stepped arrangements; andthe upper and lower levels are configured to accommodate one of thearticles placed on each of the upper and lower levels of each the firstand second two-level stepped arrangements.
 10. The transport systemaccording to claim 1, wherein a height difference between the firstbuffer and the local track in the vertical direction is the same orsubstantially the same as a height difference between the second bufferand the local track in the vertical direction.
 11. A transport systemfor addition on to an existing overhead travelling vehicle system, thetransport system comprising: a local track that is disposed so as to bebelow an overhead travelling vehicle track and above a loading port of aprocessing device from upstream of the loading port to downstream of theloading port along one direction, and is disposed in parallel orsubstantially in parallel with the overhead travelling vehicle track; alocal vehicle that travels along the local track and includes a hoistthat lifts and lowers articles; a first buffer that is disposed so as tobe below the local track and upstream of the loading port of theprocessing device along the one direction, an overhead travellingvehicle and the local vehicle both being arranged to perform deliveryand receipt of one of the articles with the first buffer; and a secondbuffer that is disposed so as to be below the local track and downstreamof the loading port of the processing device along the one direction,the overhead travelling vehicle and the local vehicle both beingarranged to perform delivery and receipt of one of the articles with thesecond buffer; wherein in a plan view of the transport system, the firstand second buffers are arranged to not overlap the loading port of theprocessing device in a vertical direction; in a side view of thetransport system, the first and second buffers are only provided eitherin front of or behind the loading port in the one direction; the firstbuffer includes a first sub-buffer and a second sub-buffer disposed in afirst two-level stepped arrangement; the second buffer includes a thirdsub-buffer and a fourth sub-buffer disposed in a second two-levelstepped arrangement; and the first and second two-level steppedarrangements each include an upper level and lower level.
 12. Atransport system to transport articles among a plurality of processingdevices, the transport system comprising: an overhead travelling vehicletrack that passes above loading ports of the plurality of processingdevices; an overhead travelling vehicle that travels in one directionalong the overhead travelling vehicle track and includes a hoist; alocal track that is disposed so as to be below the overhead travellingvehicle track and above a loading port of one of the plurality of theprocessing devices, and is disposed in parallel or substantially inparallel with the overhead travelling vehicle track; a local vehiclethat travels along the local track and includes a hoist that lifts andlowers one of the articles; and a two-level stepped buffer including anupper level and a lower level each of which is capable of accommodatingone of the articles; wherein the lower level is disposed on a sideadjacent to the loading port of the one of the processing devices, theupper level being disposed on a side spaced from the loading port, andregardless of whether one of the articles article has been placed on thelower level, the local vehicle being able to pass above the lower levelwhen the local vehicle is supporting one of the articles and when thelocal vehicle is not supporting any of the articles; and the upper levelis disposed at a height according to which the local vehicle supportingone of the articles may travel only above the upper level without any ofthe articles, and the local vehicle not supporting any of the articlesmay travel above the upper level both with one of the articles andwithout any of the articles; wherein in a plan view of the transportsystem, the first and second buffers are arranged to not overlap theloading port of the one of the processing devices in a verticaldirection; in a side view of the transport system, the first and secondbuffers are only provided either in front of or behind the loading portin the one direction; the first buffer includes a first sub-buffer and asecond sub-buffer disposed in a first two-level stepped arrangement; thesecond buffer includes a third sub-buffer and a fourth sub-bufferdisposed in a second two-level stepped arrangement; and the first andsecond two-level stepped arrangements each include an upper level andlower level.